This invention relates to tooling and method for consolidation of an article, and, more particularly, it relates to hard tooling that is reusable for consolidation of more than one article.
Certain article manufacture that includes the combination of relatively high temperature and high pressure consolidation steps requires generally inflexible, rigid tooling, sometimes referred to as hard tooling. Such tooling, generally made of an alloy based on at least one of Fe, Ni and Co for strength at high temperatures, is needed to provide support and accurate dimensions for the article during consolidation. That general type of consolidation or forming method has been widely reported under a variety of names including super plastic forming/diffusion bonding, hot isostatic pressing, vacuum hot pressing, and others. Examples of articles for the aerospace industry manufactured using one or more of such methods include, but are not limited to, composite airfoils, ducts, disks, shafts, frames, rings, shells, links, and brackets. Frequently, very close tolerances are designed in the article and required in hard tooling used during manufacture. Accordingly, the tooling can be relatively costly to manufacture.
In the manufacture of articles intended to operate at high temperatures under strenuous operating conditions, article surface contamination is to be avoided. Use of a stop-off or release type of chemical material or coating at an interface between the hard tooling and an article surface, as proposed by certain prior methods, has been observed to result in undesirable surface contamination of the article and/or delamination between plies of an article manufactured by consolidation of a plurality of superimposed plies. Therefore, such potentially contaminating substances are to be avoided between tooling and article surfaces during high temperature, high pressure consolidation. As a consequence, a surface of current hard tooling has been observed to bond with an article surface at such high temperatures and pressures. Then, to retrieve the article from the hard tooling, the tooling generally is either machined away, chemically etched away, or a combination of such methods. As a result, the relatively costly hard tooling is damaged, is not reusable and generally is destroyed.
Reported consolidation methods and tooling have included both the above described type of firm or hard tooling to which the present invention relates, as well as the generally soft tooling that is intended to be deformed during, and/or discarded after, consolidation processing. The problem of release of the article from the tooling, and of article surface contamination has been referred to in a number of U.S. patents. For example, Hodge et al in U.S. Pat. No. 3,340,053 (patented Sep. 5, 1967) during powder metal consolidation interpose a liner of Mo, W or their mixture between tungsten metal particles and an exterior casing that can contaminate the tungsten particles. In a roll diffusion bonding method, Conn, Jr., et al in U.S. Pat. No. 3,444,608and U.S. Pat. No. 3,550,252 (patented May 20, 1969 and Dec. 29, 1970, respectively) dispose a single, relatively thin foil of Ti at selective points along a mandrel to facilitate removal of a roll bonded article. Release coatings of different coefficients of thermal expansion, for example boron nitride and yttria, are described in U.S. Pat. No. 4,269,053--Agrawal et al. (patented May 26, 1981). A combination of a soft tooling disposable metal sheath with an internal coating of tantalum powder to embrittle the sheath during consolidation for ease of sheath removal is disclosed by Boncoeur et al. in U.S. Pat. No. 4,983,339 (patented Jan. 8, 1991). Cooper et al. in U.S. Pat. No. 5,069,383 (patented Dec. 3, 1991) employ a stop-off material in the form of a series of individual porous lamelar sheets disposed between stacked sheets of metal to avoid bonding between the metal sheets during conduct of a superplastic forming/diffusion bonding process. Fujikawa et al. in U.S. Pat. No. 5,096,518 and U.S. Pat. No. 5,147,086 (patented Mar. 17, 1992 and Sep. 15, 1992, respectively) use a ceramic or metal layer as a stop-off material over a material to be subjected to hot isostatic pressing.
As was mentioned above, bonding of relatively costly hard tooling to an article surface during high temperature, high pressure consolidation generally has resulted in destruction of the tooling in order to recover the consolidated article. Thus the cost of each article includes or reflects the cost of the destroyed tooling. Reusable tooling that at the same time does not contaminate an article surface can reduce the cost of an individual article, with the cost of the tooling being spread over many articles.